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Gas cap fuel pressure problem

orrum

orrum

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Orrum North Carolina
Saw a thread on here somewhere about a reference to a gas cap mod. Glad I saw it cause I just finished my setup for running a WVO blend and my Walbro was running 6-7 psi at cruising speed. I thought it should be a lil higher but I had it pulling fuel thru a 30 micron pre filter and pushing thru a add on 5 micron FFM and also pushing thru the factory FFM and filter so figured that was ok. It is completely running on my wvo blend now and I went to put some more fuel in when I got home from hauling scrap metal today and when I took the gas cap off it sucked air in! So I fueled up and left the cap real loose like in the thread and the fuel pressure went gaga! Now at idle I get 12-13 psi and cruising its 8-9 psi and WOT is 6-7 and thats all new filters and with a wvo blend in the tank. So I guess the cap is bad. So I blew thru it and sucked air thru it and it works so I put it back on and the fuel pressure went down! I changed it am running it very loose but I dont like doing that. Can I drill a hole in the bottom without going all the way thru or something?
 
You sure it's the right cap Bill? If it's a "GAS" cap instead of a diesel fuel cap, it's the wrong one. Or were you just using the vernacular "gas cap"?
 
Ha Ha Ha..... U expect me to know vernacular???? Is that something to do with horoscopes? LOl Ok its a "Diesel cap" ok. On second thought I presume its a Diesel cap.....how to tell? Nothing is easy is it when u r dealing with previous owners.
 
The fuel cap should have "Diesel Fuel only" on the top of it. The diesel caps can get gummed up with dried fuel and dirt. You might be able to soak it in a jar of gasoline to clean it up if you have the correct cap.There is a way to gut the breather in the cap but I don't know how. There probbly is a thread on it.Might be easiest to go buy a new Diesel Fuel Only cap.
 
Ok it definitely does not say diesel fuel only! Looks like they would have different threads. U reckon its a gas cap? Junkyard here I come maybe?
 
Huh mine doesn't say diesel fuel only, come to think of it I don't think any of my trucks do. I get tons of suction in my 95 6.5 (when it runs).
 
I have the reverse problem. I get pressure in the tank. It keeps the engine running when the LP dies. Check to see if it is pressure or suction - does the cap pop off or do you pull it out when hissing?
 
Great white does negative mean a sucking sound to my retarded butt? War wagon it definitely has a sucking hissing sound. It does not have pressure my old 454 dually would almost pop the cap off into ur hand so I know that feel. I am guessing it shoud not do either? It really makes a big difference to the fuel pressure with it loose versus tight!
 
Ok I thought Canadians did not have a sense of humour!!!! LOL Ok lets try this....Great White by negative pressure do u mean ur tank has a slight vacuum and upon loosening the cap u hear a slight hiss as air is drawn into the tank!!!!!
 
orrum said:
Ok I thought Canadians did not have a sense of humour!!!! LOL Ok lets try this....Great White by negative pressure do u mean ur tank has a slight vacuum and upon loosening the cap u hear a slight hiss as air is drawn into the tank!!!!!
Click to expand...

yup.

:)

We have a sense of humor, it's just a little different than our southern bros....
 
Now this is just to wierd, I just posted about BJ having a sense of humor in another thead right before I saw this.
Thats 2 things today that cracked a smile for me today BJ.
 
orrum, if you have either a gas or diesel cap, take the black outer part off, held on w/ 4 tabs on the inside where the white/yellow threaded part is. when you have the white/yellow piece in your hand, there is a spring-screen-rubber flap held in place by the little cross pieces of plastic. remove all of the guts, put the two pieces back together and there will be no more sucking, blowing on anyone's butt.
i had positive pressure on mine, i would leave it loose, it would spill fuel after a full fill up or vibrate the rest of the way off.
 
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Mine has enough pressure my tank pops when I loosen the cap IF I run it to nearly empty, if it is ~1/2 tank then it just has vaccum. I think I need to add fuel cap ectomy to my mod list.
 
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